1. Field
The teachings in accordance with the exemplary embodiments of this present disclosure generally relate to an inverter, and more particularly to a multilevel medium voltage inverter.
2. Background
In general, a multilevel medium voltage inverter is an inverter having an input power whose rms (root mean square) value is over 600V for a line-to-line voltage, and has several stages in output phase voltage. The multilevel medium voltage inverter is generally used to drive an industrial load of large inertia ranging from several kW to several MW capacities of, for a non-limiting example, fans, pumps, compressors, tractions, hoists and conveyors.
One form of multilevel inverter is a Cascaded H-Bridge (CHB) inverter architecture, which employs multiple series-connected H-Bridge inverters for driving each motor winding phase, or a cascaded NCP (Neutral Point Clamped) inverter transformed from the CHB inverter. The recently used NCP inverter is advantageous over a conventional series-connected CHB inverter due to smaller size. The multilevel inverter widely used in various fields requires a higher efficiency and a topology of smaller number of elements.
The Cascaded H-Bridge (CHB) inverter is the most common medium voltage inverter, where low voltage single phase inverters are combined to output a high voltage, and entire configuration includes an input end multi-winding transformer, unit power cells and a controller. The CHB inverter is used as a medium voltage by combining unit power cells including several low voltage single phase inverters, where unit power cells are serially connected for each phase, an output of each unit power cell is controlled to output a high voltage 3-phase voltage and power. An input power of each unit power cell of the CHB inverter must be mutually insulated, but an efficient mutual insulation of the input powers is not easy.